1. Field of the Invention
The present invention relates to a method of forming a through hole and a method of manufacturing an electronic circuit, and more particularly to a method of manufacturing a through hole in an insulating film of a wiring board and a method of manufacturing an electronic circuit using nanopaste ink.
2. Related Background Art
In an electronic circuit such as a printed wiring board, a thin film transistor (TFT), or a circuit board including a TFT, wiring made of a conductive material is generally formed on an insulating substrate. The method of manufacturing such the electronic circuit may break down into two methods: a subtractive method where a corrosion-resistant etching resist layer is provided on a conductive layer of a laminate sheet having the conductive layer deposited in advance on an insulating substrate thereof, and then the conductive layer is etched off; and an additive method where a plating resist layer is provided on an insulating substrate and a conductive layer is formed on an exposed portion of the substrate by metal plating, or the like. Now, such an etching resist layer or a plating resist layer is generally formed using a photopolymer.
In a method of forming such an etching resist layer or a plating resist layer (hereinafter referred to as an “image layer”) using a photopolymer, first, a photosensitive material such as a photopolymer is applied on a substrate such as a metal plate, paper, a laminate sheet, or an insulating substrate. Then, light is irradiated to change the solubility of the photosensitive material in a developer. Photosensitive materials include negative type ones where a portion irradiated with light is polymerized and cured to become insoluble in a developer, and positive type ones where a functional group of a portion irradiated with light is changed to become soluble in a developer. In both cases, the photosensitive material insoluble in the developer which remains on the substrate after treatment with the developer is the image layer.
Incidentally, as to an electronic circuit, in order to conform to higher density of wiring, a multilayer circuit is mainly used. In a multilayer circuit, connections between layers are made through a through hole or a via hole.
In a subtractive method of manufacturing an electronic circuit, a laminate sheet has an insulating substrate with a through hole or a via hole formed therein and a conductive layer formed on the surface of the insulating substrate including the inside of the hole. A portion of the conductive layer corresponding to a circuit portion is protected by an etching resist layer, and an unnecessary portion of the conductive layer is etched off. Here, it is necessary to ensure that the etching resist layer is formed on the conductive layer in the hole. This method requires precise control of exposure and development for image formation, and a large amount of expensive resist to be removed later is used.
As a technique of patterning an insulating film which requires no exposure treatment, a technique of forming a contact hole in an insulating film by, using inkjet, ejecting a liquid which can dissolve the insulating film is disclosed in Japanese Patent Application Laid-Open No. H10-215051.
Further, a technique of removing a liquid in a recessed shape by expanding the liquid is disclosed in Japanese Patent Application Laid-Open No. H08-117705.
However, in the conventional techniques described in the above, the processes are complicated, a large amount of waste is generated, and position control of an image pattern cannot be performed at a high level.